Field of the Invention
The invention lies in the field of semiconductor manufacture. More specifically, the invention relates to a method for fabricating a plurality of semiconductor bodies, in particular of radiation-emitting semiconductor bodies, wherein a defined sequence of semiconductor layers is deposited on a main surface of a substrate wafer.
The invention relates, in particular:
to a method for fabricating a plurality of light-emitting diode chips, in which a plurality of semiconductor layers are deposited on a main surface of a substrate wafer, and wherein at least one of the semiconductor layers includes a III-V compound semiconductor material based on GaN, such as, for example, GaN, GaAlN, InGaN, or InAlGaN; and PA1 to a method for fabricating a plurality of edge-emitting semiconductor laser chips which, on at least two mutually opposite side surfaces, have laser mirror surfaces lying plane-parallel to one another. PA1 depositing a mask layer on a main surface of a substrate wafer; PA1 forming a plurality of windows in the mask layer and uncovering the main surface of the substrate wafer within the windows; PA1 depositing a semiconductor layer sequence onto the main surface of the substrate wafer in the windows and forming substantially identical functional semiconductor structures in the windows; and PA1 dividing the wafer with the semiconductor layer sequence into a plurality of semiconductor chips by severing the wafer between the semiconductor structures.
Methods of that type are known in the art. In order to fabricate light-emitting diode chips, for example, an electroluminescent semiconductor layer sequence is grown epitaxially on a semiconductor substrate wafer. The so-called epitaxial wafer is provided with the necessary contact metallization layers for making electrical contact with the light-emitting diode chips and then divided into light-emitting diode chips by means of sawing. Similar methods are used in transistor chips, IC chips, etc.
U.S. Pat. No. 5,578,839 to Nakamura et al. (corresponding to European EP 0 599 224 A1, and U.S. Pat. Nos. 5,734,182 and 5,747,832) describes a method in which a plurality of In.sub.x Ga.sub.1-x N layers are deposited epitaxially on a substrate. The plurality of In.sub.x Ga.sub.1-x N layers forms a light-emitting diode (LED) layer sequence which extends over the entire wafer. After the deposition of the LED layer sequence, the structuring thereof by means of etching, and the application of a plurality of contact metallization layers, the wafer is divided and severed into a multiplicity of individual light-emitting diode chips by cutting through the wafer between the contact metallization layers by means of sawing, for example.
During the deposition of Ga(In,Al)N light-emitting diode structures, a particular problem exists, independently of the substrate material: the lattice constants of the nitrides differ greatly from the corresponding substrates. A further difficulty is posed by the greatly different thermal expansion coefficients of the available substrate materials (e.g. sapphire or SiC) and of the Ga(In,Al)N system. The effect of the different thermal expansions caused thereby is that when the wafer cools down from the growth temperature to room temperature, thermally induced stresses occur in the wafer. This leads to defects in the semiconductor structures, primarily cracks, holes, etc., which have a lasting adverse effect on the component properties such as ESD stability, service life, and the like.
The system Ga(In,Al)N is to be understood to mean Ga.sub.1-x-y In.sub.x Al.sub.y N where 0.ltoreq.x&lt;1, 0.ltoreq.y&lt;1 and x+y&lt;1.
A further problem in the context of Ga(In,Al)N light-emitting diode structures arises from the fact that the material system is highly stable in chemical terms. That property gives rise to major problems in the course of component structuring. Structuring of the Ga(In,Al)N layer sequences on the wafer is possible only by means of technically complicated methods, such as dry etching processes or UV-assisted wet-chemical etching processes.
In addition, sapphire and GaN, for example, can be sawn only with great technical outlay on account of their considerable hardness.
In a known method for fabricating edge-emitting laser diodes, the laser mirrors are realized, for example, by cleaving an epitaxial semiconductor wafer having the laser diode structures along the crystallographic directions of the substrate.
The fabrication of semiconductor bodies composed of a very wide variety of semiconductor materials on very different substrate crystals allows less and less the use of crystallographic directions of the substrate for producing laser mirrors by simple cleaving. Complicated techniques such as wet or dry etching processes therefore become necessary in order to realize laser mirrors in an exactly plane-parallel alignment and with little roughness. Various semiconductor material systems such as, for example, Ga(In,Al)N even have the property of being resistant to customary wet-chemical etching. In those cases, one has to rely completely on technically complicated and hence expensive dry etching processes.